This invention relates generally to systems for scrambling and unscrambling video images, and more particularly, to a system wherein scrambling is achieved by shifting a video image in time at field intervals.
A large number of methods of scrambling and unscrambling video images are currently being employed. Some of the methods are complex and expensive, are difficult to circumvent, and therefore are not easily avoided. It is, of course, desirable that a scrambling method be difficult to overcome, but it is also important that the system not be expensive or complicated, particularly at the receiving end. It is of utmost importance that the scrambling and the descrambling process not degrade image quality.
The need for inexpensive decoding is self-evident, particularly when one considers that, in modern cable televisions systems, at least one such decoder must be provided at each user site. Systems which are currently available generally require an expensive decoder, and therefore fall short of this requirement. There is, therefore, a significant need for a video scrambling and descrambling system which is secure, simple, and inexpensive to implement.
In addition to the foregoing, there is a need for a system that scrambles and unscrambles video images, and which can be employed in existing transmission and distribution without requiring extensive or expensive modifications. It would be highly advantageous if the desired system could effect unscrambling of the video image using most, if not all, of the various coding methods which are presently employed.
It is, therefore, an object of this invention to provide a system for scrambling and unscrambling which is simple and inexpensive to implement.
It is another object of this invention to provide a system for scrambling video images which does not degrade the quality of the image after unscrambling.
It is also an object of this invention to provide a video scrambling system which does not require an expensive decoder system at the user's sight.
It is a further object of this invention to provide a scrambling and descrambling system which does not intrude upon the information content of a video signal.
It is additionally an object of this invention to provide a video image scrambling system which is very difficult to circumvent.
It is yet a further object of this invention to provide a video scrambling and descrambling system which can be employed with currently available television receivers.
It is also another object of this invention to provide a video image scrambling and descrambling system which permits viewing of a high quality video image after descrambling, but precludes unauthorized copying of the transmission with the use of conventional video tape recorders.